Medical devices such as coils, tubular mesh elements and other expandable members, collectively referred to hereinafter as “embolic devices,” are often utilized for treating various types of vascular defects, particularly, aneurysms. Aneurysms are localized, blood-filled dilation of a blood vessel caused by disease, blood flow/pressure exerted in the vessel and/or weakening of the vessel wall. Aneurysm usually assumes a sac or balloon-like configuration that extends from a blood vessel. Aneurysm can rupture and cause hemorrhage, stroke (e.g., intracranial aneurysm) and other damaging consequences to the patient. During the treatment of an aneurysm, an embolic device is loaded onto a delivery system in a collapsed or radially compressed delivery configuration and then introduced into an aneurysm sac. Once delivered within the aneurysm sac, the embolic device may then expand or be expanded to an expanded configuration filling and occluding the aneurysm. Embolic devices may have a variety of sizes and shapes; however, embolic devices for treatment of aneurysm usually assume a spherical secondary configuration when deployed within the aneurysm sac. When implanted within the sac, the embolic device may further reinforce the inner walls of the aneurysm sac while occluding the aneurysm, reducing the probability of rupture or preventing further rupture of the aneurysm.
Embolic devices are commonly composed of self-expanding materials, so that when the devices are deployed from the delivery system into the target location in a patient; the unconstrained devices expand without requiring assistance. Self-expanding embolic devices may be biased so as to expand upon release from the delivery catheter and/or include a shape-memory component which allows the device to expand upon exposure to a predetermined condition. Some embolic devices may be characterized as hybrid devices which have some characteristics of both self-expandable materials and non-self-expandable materials.
Embolic devices can be made from a variety of materials, including polymers (e.g., nonbioerodable and bioerodable plastics) and metals. Bioerodable polymer embolic devices are desirable for some applications due to their biodegradeability and generally increased flexibility compared to metal embolic devices. Embolic devices can be made from shape memory or superelastic materials, such as shape memory metals (e.g., shape memory Nitinol) and polymers (e.g., polyurethane). Such shape memory embolic devices can be induced (e.g., by temperature, electrical or magnetic field or light) to take on a shape (e.g., a radially expanded shape) after delivery to a treatment site. Superelastic embolic materials, such as superelastic Nitinol, take on a shape after delivery without need for an inductive stimulus. Other devices materials include stainless steel, platinum, and Elgiloy. In drug delivery embolic devices, the device can carry and/or the surface of the device can be coated with a bioactive or therapeutic agent (e.g., thrombosis inducing agent).
Commonly used embolic devices are helical wire coil having windings dimensioned to engage the walls of the aneurysm. Although, embolic coils may migrate out of an aneurysm sac, particularly when delivered in wide neck aneurysm.
Some exemplary embolic coils are described, for instance, in U.S. Pat. No. 4,994,069, which discloses an embolic coil that assumes a linear helical configuration when stretched and a folded, convoluted configuration when relaxed. The stretched configuration is used in placing the coil at the target site (by its passage through a delivery catheter) and the coil assumes a convoluted relaxed configuration once the device is deployed at the target site. The '069 patent discloses a variety of secondary shapes of the embolic coils when deployed at the target site, such as “flower” shapes, double vortices, and random convoluted shapes. Other three-dimensional embolic coils have been described in U.S. Pat. Nos. 5,624,461 (i.e., three-dimensional in-filling embolic coil), 5,639,277 (i.e., embolic coils having twisted helical shapes) and 5,649,949 (i.e., variable cross-section conical embolic coils). Embolic coils having little or no inherent secondary shape have also been described, such as in U.S. Pat. Nos. 5,690,666 and 5,826,587.
Spherical shaped embolic devices are described in U.S. Pat. No. 5,645,558, which discloses that one or more strands can be wound to form a substantially hollow spherical or ovoid shape comprising overlapping strands when deployed in an aneurysm. Other embolic devices that assume spherical shapes when deployed are described in U.S. Pat. No. 8,998,947, which discloses tubular mesh having petal-like sections to form a substantially spherical shape having overlapping petals-like sections when deployed in an aneurysm.
A variety of delivery assemblies for embolic devices are known. For instance, U.S. Pat. Nos. 5,250,071 (i.e., interlocking clasps), 5,312,415 (i.e., interconnecting guidewire to deliver multiple coils), and 5,354,295 and 6,425,893, to Guglielmi (i.e., electrolytic detachment).